Glycogen synthase kinase 3 (GSK3) is a proline-directed serine/threonine kinase originally identified as an activity that phosphorylates glycogen synthase as described in Woodgett, Trends Biochem Sci, 16: 177-181 (1991). GSK3 consists of two isoforms, .alpha. and .beta., and is constitutively active in resting cells, inhibiting glycogen synthase by direct phosphorylation. Upon insulin activation, GSK3 is inactivated, thereby allowing the activation of glycogen synthase and possibly other insulin-dependent events. Subsequently, it has been shown that GSK3 is inactivated by other growth factors or hormones that, like insulin, signal through receptor tyrosine kinases. Examples of such signaling molecules include IGF-1 and EGF as described in Saito et al, Biochem J, 303: 27-31 (1994), Welsh et al, Biochem J, 294: 625-629 (1993), and Cross et al, Biochem J, 303: 21-26 (1994). GSK3 has been shown to phosphorylate .beta.-catenin as described in Peifer et al, Develop Biol 166:543-56 (1994). Other activities of GSK3 in a biological context include GSK3's ability to phosphorylate tau protein vitro as described in Mandelkow and Mandelkow, Trends in Biochem Sci 18: 480-83 (1993), Mulot et al, Febs Lett 349: 359-64 (1994), and Lovestone et al, Curr Biol 4: 1077-86 (1995), and in tissue culture cells as described in Latimer et al, Febs Lett 365: 42-6 (1995). Selective inhibition of GSK3 may be useful to treat or inhibit disorders mediated by GSK3 activity.